Numerous pipelines are widely distributed in ceilings, walls and floors of nuclear power plants, such as waste water drain pipes, water supply pump pipes, reactor drain pipes, safety injection pump drain pipes, drain ways of the valve housings, and the pumping rooms of the fuel pools.
Affected by radioactive materials, the inside of the pipeline is radioactively contaminated. When the radioactivity of the pipelines is contaminated to the extent that it needs to be decontaminated or scrapped, the pipelines will be removed. Hence, during the maintenance or the preparation for decommissioning of the nuclear power plant, the extent of radioactivity contamination of each pipelines will be measured.
The calibration and measurement for pipelines radioactivity contamination are multi-selective, e.g., smear sampling method, γ-spectrum analysis, scraping sampling with radiochemical analysis, and total acid etching method.
However, in the traditional measurement, the object sampled by the measurement is only part of the pipelines, so as the measurement result is not representative. Although γ-spectrum analysis is capable of measuring the radioactive activity of all parts of the pipeline from the outside of the pipeline, it is difficult to calibrate the measurement results due to the various shapes of the pipelines, so as the correct radioactivity cannot be measured.